This invention relates to a microscope substage-illumination illuminator with a variable field stop.
According to the rules of Kohler illumination, a variable mechanical field stop is focused into the plane of the specimen by the optical elements of an illuminator (condenser). The luminous field in the object is stopped down by means of a field stop so that it conforms to the field of view taken by the objective and viewed in the eyepiece.
Since, when observing transmitted light, illuminator and viewing means are separate components, the optical axes of both elements must be in line with one another. In particular, in the case of interchangeable condensers, adjusting means are provided by which the field stop in the specimen plane can be positioned in relation to the field of view of the observation means.
In prior art adjusting methods, one of the lenses or a tilting mirror, which focuses the field stop, is moved. However, the prior art techniques have the disadvantage of altering the optical axis of the illuminating beam's path, giving rise to what is known as oblique illumination.
New devices employing these techniques have been suggested for altering the position of the field stop in the illuminator by means of additional special adjusting means or by relocating the condenser altogether. However, since in many cases the person using the microscope must adjust the position of the field stop and its size for best possible illumination of the object field, it is inconvenient for him to operate a variety of controls independently of one another. In particular, if only minor corrections of the position of the field stop are necessary after a change of objective, he will confine himself to adjusting the size of the field stop and neglect to correct the position.